The present invention relates to an electronic device such as a video display device capable of measuring and displaying its cumulative operating time or the time that it has had power applied to it. An accurate measure and display of this power-on time can be invaluable information when servicing or troubleshooting the device. Also, it can assist in forecasting future spare parts requirements by providing information necessary to calculate their mean time between failures.
One way of obtaining this cumulative power-on information for a color video display device using a cathode-ray tube (CRT), for example, is to measure and update this information by writing it in a nonvolatile memory every 30 minutes, and then beginning a new measuring cycle. When needed, the accumulated measured values are read out from the nonvolatile memory and, if desired, used for calculating the life span of the device or for some other related service feature.
When the power-on time is periodically updated, for example every 30 minutes, such update must be written into the nonvolatile memory during a finite period of time. If for a variety of reasons, like a power surge or failure, an electric shock occurs in the nonvolatile memory, in the microcomputer or in the interconnecting signal lines during this finite period of time, erroneous information could be written into the nonvolatile memory resulting in the loss of this valuable cumulative power-on time information.